An improved vibration technique for enhancing temperature uniformity and heat transfer in viscous fluid flow

Radial heat transfer in viscous pipe flow is controlled by thermal conduction which leads to a wide radial temperature distribution and slow heating of the core region of the flow. This is highly undesirable in many industrial processes as it results in a grossly uneven distribution of fluid heat treatment. The use of static in-line mixers to promote radial mixing and, thus, heat transfer and temperature uniformity, engenders large pressure drops and the devices are generally prohibited in processes where hygiene is paramount as they are difficult to keep clean. We recently reported a Computational Fluid Dynamics (CFD) study which showed that the superimposing of transverse mechanical oscillations on the steady flow of a viscous fluid in a pipe with an isothermal wall, results in a large enhancement in wall heat transfer, as well as a considerably more uniform radial temperature distribution accompanied by rapid heating of the inner region of the flow. Such a transverse vibration also causes the thermal boundary layer to grow more rapidly and, thus, the temperature profile to develop very rapidly in the axial direction. In this article, we report on an enhanced vibration technique which combines transverse oscillations with a step rotation of oscillation orientation. The technique produces much more improved effects compared to transverse vibration alone, and it also excels in comparison with the well-known Kenics helical static mixer.